I kind of like this idea. In all honesty, if Nolan truly wants his movies to be realistic then what's more realistic than the death of a vigilante? In the real world, I don't think an actual vigilante would survive as long as Batman has already. He's just one man. Sooner or later he is bound to make a mistake which will cause his downfall.

He becomes more experienced as he goes along. He would probably be more likely to make one of those mistakes early on. If he just randomly dies from a mistake in the middle of his career, it sort of implies he'd been relying on luck to a larger degree the entire time. Now if he sacrificed himself, that would be different.